U.S. patent application number 12/225277 was filed with the patent office on 2010-07-15 for method of testing transmission of compressed digital video for iptv.
This patent application is currently assigned to KONINKLIJKE KPN N.V.. Invention is credited to Menno Remco Bangma, John Gerard Beerends, Jeroen Martijn Van Vugt.
Application Number | 20100177196 12/225277 |
Document ID | / |
Family ID | 36702657 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100177196 |
Kind Code |
A1 |
Beerends; John Gerard ; et
al. |
July 15, 2010 |
Method of Testing Transmission of Compressed Digital Video for
IPTV
Abstract
The invention relates to a digital video test sequence
comprising an intra coded picture (I) and a plurality of predicted
pictures (P, B) following said intra coded picture. Each of said
intra coded picture and predicted pictures comprises a luminance
component (Y) and two chrominance components (Cr, Cb). A variation
in at least one of the chrominance components between at least two
successive pictures is uncorrelated with a variation in the
luminance component between said successive pictures for at least a
portion of a display panel on which said pictures are to be
displayed. The video test sequence can be used in detecting packet
loss for IPTV data connections.
Inventors: |
Beerends; John Gerard;
(Hengstdijk, NL) ; Bangma; Menno Remco; (Nootdorp,
NL) ; Van Vugt; Jeroen Martijn; (The Hague,
NL) |
Correspondence
Address: |
MICHAELSON & ASSOCIATES
P.O. BOX 8489
RED BANK
NJ
07701-8489
US
|
Assignee: |
KONINKLIJKE KPN N.V.
The Hague
NL
|
Family ID: |
36702657 |
Appl. No.: |
12/225277 |
Filed: |
March 27, 2007 |
PCT Filed: |
March 27, 2007 |
PCT NO: |
PCT/EP2007/002727 |
371 Date: |
October 3, 2008 |
Current U.S.
Class: |
348/192 ;
348/180; 348/E17.001 |
Current CPC
Class: |
H04N 21/64322 20130101;
H04N 17/004 20130101; H04N 21/44008 20130101; H04N 19/89 20141101;
H04N 21/44209 20130101 |
Class at
Publication: |
348/192 ;
348/180; 348/E17.001 |
International
Class: |
H04N 17/00 20060101
H04N017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2006 |
EP |
06075712.7 |
Claims
1. A digital video test sequence comprising an intra coded picture
(I) and a plurality of predicted pictures (P, B) following said
intra coded picture, each of said intra coded picture and predicted
pictures comprising a luminance component (Y) and two chrominance
components (Cr, Cb), wherein a variation in at least one of the
chrominance components between at least two successive pictures is
uncorrelated with a variation in the luminance component between
said successive pictures for at least a portion of a display panel
on which said pictures are to be displayed.
2. The video test sequence according to claim 1, comprising an
intra coded picture (I) and a plurality of predicted pictures (P,
B) following said intra coded picture, each of said intra coded
picture and predicted pictures comprising a luminance component (Y)
and two chrominance components (Cr, Cb), wherein a variation in at
least one of the chrominance components between at least two
successive pictures is uncorrelated with a variation in the
luminance component between said successive pictures for at least a
portion of a display panel on which said pictures are to be
displayed, and the first picture of said test sequence is said
intra coded picture (I) and said predicted pictures (P) are free of
intra coded information.
3. The video test sequence according to claim 1, wherein each of
said intra coded picture (I) and plurality of predicted pictures
(P,B) comprises a plurality of blocks of pixels forming
respectively said intra coded pictured and predicted pictures on
said display panel and wherein a predicted picture has been
established by a prediction of substantially all blocks of a
preceding picture.
4. The video test sequence according to claim 1, wherein said
variation of said luminance component (Y) is zero and said
variation of said chrominance components (Cr, Cb) is non-zero.
5. The video test sequence according claim 4, wherein at least one
of said chrominance components (Cr, Cb) of said successive pictures
(I, P, B) alternate between two values.
6. A method of testing a digital data connection between a
transmitting end and a receiving end of said, data connection, said
method comprising the steps of: transmitting a digital video test
sequence over said data connection from said transmitting end to
said receiving end of said data connection, wherein said digital
video test sequence comprises an intra coded picture (I) and a
plurality of predicted pictures (P, B) following said intra coded
picture, each of said intra coded picture and predicted pictures
comprising a luminance component (Y) and two chrominance components
(Cr, Cb), wherein a variation in at least one of the chrominance
components between at least two successive pictures is uncorrelated
with a variation in the luminance component between said successive
pictures for at least a portion of a display panel on which said
pictures are to be displayed.
7. The method according to claim 6, of testing a digital data
connection between a transmitting end and a receiving end of said
data connection, said method comprising the steps of: transmitting
a digital video test sequence over said data connection from said
transmitting end to said receiving end of said data connection,
wherein said digital video test sequence comprises an intra coded
picture (I) and a plurality of predicted, pictures (P, B) following
said intra coded picture, each of said intra coded picture and
predicted pictures comprising a luminance component (Y) and two
chrominance components (Cr, Cb), wherein a variation in at least
one of the chrominance components between at least two successive
pictures is uncorrelated with a variation in the luminance
component between said successive pictures for at least a portion
of a display panel on which said pictures are to be displayed;
receiving said video test sequence at a receiving end of said data
connection; having said video test sequence displayed on a display
panel at said receiving end; and evaluating said pictures on said
display panel to observe errors in transmitting of said video test
sequence.
8. The method according to claim 7, wherein said method further
comprises the step of assessing the area on said display panel on
which said pictures (I, P, B) are displayed incorrectly with regard
to said variations of said luminance component (Y) and said
chrominance components (Cr, Cb) between successive pictures and
correlating said area with a number of transmitting errors over
said digital data connection.
9. The method according to claim 6, wherein said digital data
connection forms part of a connectionless network.
10. The method according to claim 6, using a digital video test
sequence comprising an intra coded picture (I) and a plurality of
predicted pictures (P, B) following said intra coded picture, each
of said intra coded picture and predicted pictures comprising a
luminance component (Y) and two chrominance components (Cr, Cb),
wherein variation in at least one of the chrominance components
between at least two successive pictures is uncorrelated with a
variation in the luminance component between said successive
pictures for at least a portion of a display panel on which said
pictures are to be displayed, and the first picture of said test
sequence is said intra coded picture (I) and said predicted
pictures (P) are free of intra coded information.
11. A system arranged for testing a digital data connection between
a transmitting end and a receiving end of said data connection,
wherein said system is arranged for transmitting a digital video
test sequence over said data connection from said transmitting end
to said receiving end of said data connection, wherein said digital
video test sequence comprises an intra coded picture (I) and a
plurality of predicted pictures (P, B) following said intra coded
picture, each of said intra coded picture and predicted pictures
comprising a luminance component (Y) and two chrominance components
(Cr, Cb), wherein a variation in at least one of the chrominance
components between at least two successive pictures is uncorrelated
with a variation in the luminance component between said successive
pictures for at least, a portion of a display panel on which said
pictures are to be displayed.
12. The system according to claim 11, wherein said system is
further arranged for performing the method of testing a digital
data connection between a transmitting end and a receiving end of
said data connection, said method comprising the steps of:
transmitting a digital video test sequence over said data
connection from said transmitting end to said receiving end of said
data connection, wherein said digital video test sequence comprises
an intra coded picture (I) and a plurality of predicted pictures
(P, B) following said intra coded picture, each of said intra coded
picture and predicted pictures comprising a luminance component (Y)
and two chrominance components (Cr, Cb), wherein a variation in at
least one of the chrominance components between at least two
successive pictures is uncorrelated with a variation in the
luminance component between said successive pictures for at least a
portion of a display panel on which said pictures are to be
displayed; receiving said video test sequence at a receiving end of
said data connection; having said video test sequence displayed on
a display panel at said receiving end; and evaluating said pictures
on said display panel to observe errors in transmitting of said
video test sequence.
13. A broadcast test channel arranged for transmitting the digital
video test sequence according to claim 1 over a network.
14. A server arranged for broadcasting, multicasting and/or
unleashing the digital video test sequence according to claim 1
over a network to a client.
15. An encoder device arranged for composing a digital video test
sequence according to claim 1, wherein a first picture of said
sequence is an intra coded picture (I) and all subsequent pictures
are predicted pictures (P, B).
16. The encoder device according to claim 15, wherein said encoder
device is arranged such that each predicted picture (P, B) is free
of intra coded information.
Description
FIELD OF THE INVENTION
[0001] In general, the invention relates to the field of testing a
digital data connection. More specifically, the invention relates
to the field of evaluating packet loss during communication over a
digital data connection by means of a digital video test
sequence.
BACKGROUND OF THE INVENTION
[0002] Within the next few years, multiple suppliers will offer
television via xDSL data connections. Such services are generally
known as IPTV. With IPTV, pictures on a display panel are built
from data packets received by a decoder over the xDSL data
connection.
[0003] IPTV is very sensitive to the quality of the data
connection. Noise and too far a distance from a transmitting end
may significantly reduce the quality of the picture displayed on
the display panel. However, the loss of data packets between the
transmitting end and the decoder provides for the most detrimental
reduction in quality of the picture, since packet loss results in a
disturbed pictures. As an indication, the forum concerned with
Digital Video Broadcasting (DVB-forum) prescribes a maximum of one
noticeable artifact per hour.
[0004] It is known in the art to provide dedicated devices to
measure packet loss over data connections. However, these devices
are complicated and may only be operated by trained experts. Only
these experts are capable of determining the quality of the data
connection by using these dedicated devices.
[0005] There exists a need in the art for a less complicated way of
testing the quality of a data connection for use in IPTV
services.
[0006] SUMMARY OF THE INVENTION
[0007] A digital video test sequence is proposed that comprises an
intra coded picture and a plurality of predicted pictures following
said intra coded picture. Each of said intra coded picture and
predicted pictures comprises a luminance component and two
chrominance components. A variation in at least one of the
chrominance components between at least two successive pictures is
uncorrelated with a variation in the luminance component between
said successive pictures for at least a portion of a display panel
on which said pictures are to be displayed.
[0008] Furthermore, a method of testing a digital data connection
between a transmitting end and a receiving end of said data
connection is proposed. The method involves transmitting a digital
video test sequence over said data connection from said
transmitting end to said receiving end of said data connection. The
digital video test sequence comprises an intra coded picture and a
plurality of predicted pictures following said intra coded picture.
Each of said intra coded picture and predicted pictures comprises a
luminance component and two chrominance components. A variation in
at least one of the chrominance components between at least two
successive pictures is uncorrelated with a variation in the
luminance component between said successive pictures for at least a
portion of a display panel on which said pictures are to be
displayed.
[0009] Still further, a system is proposed that is arranged for
testing a digital data connection between a transmitting end and a
receiving end of said data connection. The system is arranged for
transmitting a digital video test sequence over said data
connection from said transmitting end to said receiving end of said
data connection. The digital video test sequence comprises an intra
coded picture and a plurality of predicted pictures following said
intra coded picture. Each of said intra coded picture and predicted
pictures comprises a luminance component and two chrominance
components. A variation in at least one of the chrominance
components between at least two successive pictures is uncorrelated
with a variation in the luminance component between said successive
pictures for at least a portion of a display panel on which said
pictures are to be displayed.
[0010] A picture on a display panel is typically built from a
plurality of data packets transmitted over a data connection. If
one of the packets is lost between the transmitting end and the
receiving end (the decoder), insufficient information is available
to display the entire new picture on the display panel. In this
situation, the decoder will try to `repair` the picture by
displaying a part of the preceding picture or a part from adjacent
macro blocks to fill in the gap in the new picture associated with
the lost data packet. The motion of the part of the preceding
picture is predicted by evaluating the motion of the parts of the
picture surrounding the missing part.
[0011] To provide an encoded video sequence, typically a
transformation is made from the primary colors of the picture to a
luminance component Y and two color difference components Cb and
Cr. These color difference components are also referred to as
chrominance components. In a conventional video sequence comprising
a plurality of pictures, there exists a correlation between the
luminance component Y and the chrominance components Cb and Cr for
each picture.
[0012] The invention is based on the insight that in encoded video
sequences, the prediction of a picture from a preceding picture
(field or frame) is performed solely on the basis of the luminance
component of the picture. By providing an encoded video sequence
over a data connection, wherein the luminance component and the
chrominance components of a picture are uncorrelated, packet loss
over the data connection will be visible on the display panel as a
part with a color difference as compared to the remaining part of
the display panel. In other words, the repair strategies of the
decoder are used to visualize the packet loss. The display panel
part with the color difference is indicative of a packet loss,
associated with said part, over the data connection. Loss of only a
single packet may already be clearly visible on the display panel.
Consequently, by transmitting the video sequence over the data
connection, the quality of the data connection can be simply tested
by looking at the display panel showing the pictures of the video
sequence.
[0013] In an embodiment of the invention, the first picture of the
test sequence is the intra coded picture and the predicted pictures
are free of intra coded information. This embodiment is
advantageous in that the packet loss will remain visible on the
display panel, since no full refreshment of the picture will occur
after displaying the intra coded picture. Consequently, the person
assessing the quality of the data connection may simply switch on
the display panel and come back whenever he desires to evaluate the
result.
[0014] In an embodiment of the invention, each of the intra coded
picture and plurality of predicted pictures comprises a plurality
of blocks of pixels forming, respectively, the intra coded pictured
and predicted pictures on the display panel. The predicted picture
is established by a prediction of substantially all blocks of a
preceding picture. This embodiment has the advantage that each
packet loss will be visible on the display panel. It will be clear
to the skilled person that, whenever loss of a packet influences
more than one block of pixels on the display panel, it is not
necessary that all blocks of the new picture are established by
prediction on the basis of all of the blocks of the preceding
picture.
[0015] In an embodiment of the invention, the variation of the
luminance component is zero and the variation of said chrominance
components is non-zero. A video sequence with a static luminance
component can easily be encoded by an encoder that uses the
variation in the luminance component (that is absent in this
embodiment, i.e., zero motion) for motion prediction of the next
picture. The chrominance components are then encoded as chrominance
difference signals. Preferably, the chrominance components of said
successive pictures are alternating between two values (preferably,
a maximum variation between these values is used) since then loss
of a data packet on the data connection is clearly visible on the
display panel by a significant color difference of the part
associated with the lost packet.
[0016] In an embodiment of the invention, the method involves
receiving the video test sequence at a receiving end of the data
connection and displaying the video test sequence on the display
panel at the receiving end. The pictures are evaluated to observe
errors in transmitting of said video test sequence. This method is
advantageous in that customers may themselves evaluate the quality
of the data connection with their decoder.
[0017] In an embodiment of the invention, the method further
involves assessing the area on the display panel on which said
pictures are displayed incorrectly with regard to said variations
of said luminance component and said chrominance components between
successive pictures. The area is correlated with a number of
transmitting errors, i.e., packet loss, over the digital data
connection. By assessing the area of the display panel that shows
incorrect pictures, a quantitative measure can be obtained for the
quality of the data connection.
[0018] The digital data connection may be a connectionless network.
The risk of packet loss is highest in such networks.
[0019] The invention also relates to a broadcast test channel
arranged for transmitting the digital video test sequence as
discussed above. The broadcast test channels allows consumers to
evaluate the data connection at any time they desire to do so.
[0020] The invention also relates to a server arranged for
broadcasting, multicasting and/or unicasting the digital video test
sequence as discussed above. A customer may retrieve the digital
test sequence from the server to test the quality of his data
connection.
[0021] The invention also relates to an encoder device arranged for
composing the digital video test sequence discussed above, wherein
a first picture of said sequence is an intra coded picture and all
subsequent pictures are predicted pictures. Each predicted picture
is free of intra coded information. The chrominance variations are
then encoded solely on the basis of the difference between
successive pictures and the video sequence will not erase a part on
the display panel corresponding with a packet loss over the data
connection. The resulting video sequence can be predicted easily by
the decoder, by ensuring that the luminance variation is zero (no
motion) or substantially zero (slow motion) between successive
pictures.
[0022] It should be noted that the above defined embodiments, and
aspects thereof, may be combined.
[0023] The invention will be further illustrated with reference to
the attached drawings, which schematically show a preferred
embodiment according to the invention. It will be understood that
the invention is not in any way restricted to this specific and
preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In the drawings:
[0025] FIGS. 1A and 1B schematically illustrate, respectively, a
video sequence of the prior art and according to an embodiment of
the invention;
[0026] FIG. 2 illustrates a system comprising a data connection to
be tested with the video sequence of FIG. 1B; and
[0027] FIGS. 3A-3C schematically illustrate a display panel
displaying a video test sequence transmitted over the data
connection of FIG. 2.
DETAILED DESCRIPTION OF THE DRAWINGS
[0028] Digital video sequences comprise a series of moment pictures
(frames or fields). The display panel for displaying the video
sequence comprises multiple points on a lattice, which are called
pixels. Each picture comprises digital data corresponding to the
pixels, and each digital data indicates the color, brightness, or
gradation value of the corresponding pixel. Pixels may be grouped
in blocks of pixels, also referred to as macro blocks. The digital
video sequence has a form of the bit sequence produced by
compressing the original video data.
[0029] The known international standards relating to the video are
(i) MPEG-2 (MPEG: moving picture experts group) and MPEG-4 based on
ISO (international organization for standardization) and IEC
(international electrotechnical commission) which are international
standardizing organizations, that is, MPEG-2 is defined as
ISO/IEC-13818, and MPEG-4 is defined as ISO/IEC-14496, and (ii)
H.261 and H263 based on ITU (international telecommunication union)
recommendation, among others. The skilled person is assumed to be
familiar with the above standards. A short summary of the MPEG
compression of digitized pictures is provided in U.S. Pat. No.
6,545,727.
[0030] As an example of the video data coding methods used in the
international standards, the interframe prediction coding method is
known. In this method, differences between two pictures which are
close to each other are encoded and transmitted, and in the
receiving side, only the difference is decoded and is added to a
picture which has already been decoded. Statistically, such
adjacent pictures tend to include the same objects or backgrounds;
that is, in most cases, the adjacent pictures resemble each other
and have only slight differences. Therefore, data can be compressed
by actually encoding only such a slight difference.
[0031] FIG. 1A shows an example of a conventional video sequence
comprising I-pictures (Intra Coded Frame or Field), B-pictures
(Bi-directionally Predicted Frame or Field) and P-pictures
(Predicted Frame or Field). The I-pictures are coded in a fully
independent mode. The P-pictures are coded with respect to a
preceding I- or P-picture in the sequence. The B-pictures are coded
with respect to two pictures of the I- or P-kind, which are the
preceding one and the following one in the video sequence. The
order of the pictures in the sequence corresponds to the order in
which the pictures are displayed on a display panel. Since a
picture may comprise one or more errors, the prediction mechanism
may result in a propagation of the error. In order to avoid such a
propagation, the conventional video sequence has several I-pictures
to refresh the entire picture.
[0032] As already mentioned in the introduction, for each picture a
transformation is made from the primary colors of the picture to a
luminance component or signal Y and two color difference components
or signals Cb and Cr. The color difference components are also
referred to as chrominance components. In a conventional video
sequence comprising a plurality of pictures, there exists a
correlation between the luminance component Y and the chrominance
components Cb and Cr for each picture I, P, B.
[0033] FIG. 1B illustrates an encoded video sequence 1 according to
an embodiment of the invention. The digital video sequence 1
comprises an intra coded picture I and a plurality of predicted
pictures P following the intra coded picture I. Each of the intra
coded picture I and predicted pictures P comprise a luminance
component Y and two chrominance components Cb, Cr. The variation in
at least one of the chrominance components Cb, Cr between at least
two successive pictures (I-P or P-P)is controlled such that this
variation is uncorrelated with a variation in the luminance
component between the successive pictures for at least a portion of
a display panel on which the pictures are displayed. The variation
in the chrominance is indicated by the successive black and white
pictures in FIG. 1B. It has been found that such a video sequence
can be advantageously applied for testing the quality of a data
connection, as will be further described with reference to FIGS. 2
and 3A-3C.
[0034] It should be appreciated that various alternatives of the
video sequence 1 of FIG. 1B are possible that fall within the scope
of the present invention.
[0035] As an example, one or more of the P-pictures may be replaced
by B-pictures. Furthermore, it is not necessary that the
correlation between the variation of the luminance components and
chrominance components is absent between each pair of successive
pictures. Still further, the video sequence 1 of FIG. 1 may include
further I-pictures, since it is sufficient that the variation of
the chrominance components of two pictures is uncorrelated with the
variation in the luminance components of these two pictures of the
sequence for a plurality of pictures. The absence of the
correlation results in a picture error on the display panel that
displays the video sequence. The absence of further I-pictures in
the sequence ensures that a picture error resulting from a packet
loss is not erased by such further I-pictures.
[0036] FIG. 2 shows a system 10 for testing a data connection 11
capable of transmitting data packets for IPTV. The data connection
11 may be part of a connectionless network, such as the internet. A
server 12 comprises a database 13 with one or more video test
sequences 1 as depicted in FIG. 1B. The encoded digital video test
sequence is provided by an encoder 14 that may be part of the
server 12. The server 12 further comprises a processor 15 for
replying to requests of clients.
[0037] An example of such a client comprises a decoder 20 capable
of communicating with the server 12 over the data connection 11.
The decoder 20 is further connected to a display apparatus 21
capable of displaying pictures presented to the decoder 20.
[0038] It should be appreciated that the system 10 may have a
different architecture. For instance, the system may include a
broadcasting station (not shown) that transmits a continuous
broadcast signal with the video test sequence that can be picked up
by the decoder 21.
[0039] The operation of the system 10 of FIG. 2 will now be
explained with reference to FIGS. 3A-3C.
[0040] The video test sequence of FIG. 1B is transmitted over the
data connection 11 in several packets. Each picture I, P is built
from several packets. The packets generally comprise a header that
indicates the type of picture (I or P) and a payload with the
display data.
[0041] The first picture of FIG. 3A is an I-picture. The picture is
built from the display data of several data packets send over the
data connection 11. The header of each of the data packets
indicates that the packet comprises information for an I-picture,
whereas the payload comprises the encoded luminance component Y and
chrominance components Cr, Cb for the I-picture. As an example, the
I-picture of the video sequence has a luminance component Y=60 and
chrominance components Cr=40, Cb=20. A picture with the luminance
component and chrominance components will be displayed on the
display panel 21, as illustrated
[0042] The next picture is a predicted picture P. In order to
illustrate the present embodiment of the invention, it is assumed
that a packet carrying information of the predicted picture P is
lost during transmission over the data connection 11. In the
present embodiment of the invention, the variation of the luminance
component Y is kept zero, i.e., Y=60 for the P-picture of the video
test sequence. However, the chrominance components Cr, Cb of the
video test sequence are not correlated to the variation in the
luminance component and are set to a significant variation, e.g.,
Cr=20, Cb=40. As the data packet is lost during transmission,
however, the corresponding part 22 on the display panel 21 will
remain with Y=60, Cr=40 and Cy=20. The decoder 20 will try to
repair the effect of the lost data packet by using the data of the
previous I-picture. As the decoder 20 only uses the prediction of
the variation of the luminance component Y (which is zero) for
further error correction, the block(s) of pixels associated with
the lost data packets will simply display the information of the
previous I-picture. This is shown in FIG. 3B.
[0043] The next picture P in the video sequence has a luminance
component Y=60 (static luminance) and chrominance components Cr=40,
Cb=20. It is assumed that the data packets for this picture all
arrive at the decoder 20. The display panel 21 will display a
picture P with a luminance component of Y=60 and chrominance
components Cr=40, Cb=20. However, for the part 22 that had an error
due to the packet loss, the chrominance components will be
different, i.e., Cr=60, Cb=0. Consequently, the packet loss of the
preceding picture remains visible, as shown in FIG. 3C.
[0044] It should be appreciated that, preferably, the predicted
pictures P are free of intra coded information. This avoids that
the error part 22 is erased.
[0045] Typically, the intra coded picture I and predicted pictures
P comprises a plurality of blocks of pixels (macro blocks). In
order to ensure that each data packet loss is detected, it is
preferred that a predicted picture P has been established by a
prediction of substantially all blocks of a preceding picture I or
P. However, whenever loss of a packet influences more than one
block of pixels on the display panel 21, it is not necessary that
the new picture is established by prediction on the basis of all
blocks of the preceding picture.
[0046] It will be clear that receiving the video test sequence 1 at
the decoder 20 and displaying the sequence on the display panel 21
allows a customer to evaluate the pictures on the display device 21
to observe errors in transmitting packets of the video test
sequence 1 over the data connection 11.
[0047] Apart from evaluating the quality of the data connection 11
by viewing the effect of packet loss on the display panel 21, it is
also possible to extract some quantitative information for the
picture on the display panel 21. As an example, if one determines
the area of the display panel 21 that displays the pictures
incorrectly, this measure provides information on the number of
data packets lost. If a customer finds, e.g., that after three
hours the display panel of FIG. 3C is displayed on his display
panel 21, he may conclude that in the past three hours a single
data packet was lost. If he would have found four or such areas,
this may indicate that four packets were lost during the
measurement period. Of course, if by coincidence the data packets
responsible for filling the same part of the display panel are
lost, this may not be visible on the display panel 21.
[0048] It should be appreciated that the invention is not limited
by the embodiment described above. It is the gist of the invention
to provide for a video sequence comprising at least two successive
predicted pictures, wherein these successive pictures are
uncorrelated in space and/or time. The absence of a correlation
between the successive pictures prevents the decoder 20 to correct
errors resulting from packet loss.
* * * * *